Description

D = fdesign.bandstop(SPEC) constructs
object D and sets the Specification property
to SPEC. Entries in SPEC represent
various filter response features, such as the filter order, that govern
the filter design. Valid entries for SPEC are shown
below. These entries are not case sensitive.

Note

Specification options marked with an asterisk require the DSP System
Toolbox™ software.

'Fp1,Fst1,Fst2,Fp2,Ap1,Ast,Ap2' (default
spec)

'N,F3dB1,F3dB2'

'N,F3dB1,F3dB2,Ap' *

'N,F3dB1,F3dB2,Ap,Ast' *

'N,F3dB1,F3dB2,Ast' *

'N,F3dB1,F3dB2,BWp' *

'N,F3dB1,F3dB2,BWst' *

'N,Fc1,Fc2'

'N,Fc1,Fc2,Ap1,Ast,Ap2'

'N,Fp1,Fp2,Ap'

'N,Fp1,Fp2,Ap,Ast'

'N,Fp1,Fst1,Fst2,Fp2'

'N,Fp1,Fst1,Fst2,Fp2,C' *

'N,Fp1,Fst1,Fst2,Fp2,Ap' *

'N,Fst1,Fst2,Ast'

'Nb,Na,Fp1,Fst1,Fst2,Fp2' *

The filter specifications are defined as follows:

Ap — amount of ripple allowed
in the passband in decibels (the default units). Also called Apass.

Ap1 — amount of ripple allowed
in the pass band in decibels (the default units). Also called Apass1.

Ap2 — amount of ripple allowed
in the pass band in decibels (the default units). Also called Apass2.

Ast — attenuation in the
first stopband in decibels (the default units). Also called Astop1.

C — Constrained band flag.
This enables you to specify passband ripple or stopband attenuation
for fixed-order designs in one or two of the three bands.

In the specification 'N,Fp1,Fst1,Fst2,Fp2,C',
you cannot specify constraints simultaneously in both passbands and
the stopband. You can specify constraints in any one or two bands.

F3dB1 — cutoff frequency
for the point 3 dB point below the passband value for the first cutoff.

F3dB2 — cutoff frequency
for the point 3 dB point below the passband value for the second cutoff.

Fc1 — cutoff frequency for
the point 6 dB point below the passband value for the first cutoff.
(FIR filters)

Fc2 — cutoff frequency for
the point 6 dB point below the passband value for the second cutoff.
(FIR filters)

Fp1 — frequency at the start
of the pass band. Also called Fpass1.

Fp2 — frequency at the end
of the pass band. Also called Fpass2.

Fst1 — frequency at the
end of the first stop band. Also called Fstop1.

Fst2 — frequency at the
start of the second stop band. Also called Fstop2.

N — filter order.

Na — denominator order for
IIR filters.

Nb — numerator order for
IIR filters.

Graphically, the filter specifications look similar to those
shown in the following figure.

Regions between specification values like Fp1 and Fst1 are
transition regions where the filter response is not explicitly defined.

The filter design methods that apply to a bandstop filter specification
object change depending on the Specification. Use designmethods to determine which design
methods apply to an object and the Specification property
value.

Use designopts to determine
the design options for a given design method. Enter help(D,METHOD) at
the MATLAB® command line to obtain detailed help on the design
options for a given design method, METHOD.

D = fdesign.bandstop(specvalue1,specvalue2,specvalue3,specvalue4,...
specvalue5,specvalue6,specvalue7) constructs
an object D with the default Specification property,
using the values you provide in specvalue1,specvalue2,specvalue3,specvalue4,specvalue5,
specvalue6 and specvalue7.

D = fdesign.bandstop(...,Fs) adds
the argument Fs, specified in Hz to define the
sampling frequency. If you specify the sampling frequency as a trailing
scalar, all frequencies in the specifications are in Hz as well.

D = fdesign.bandstop(...,MAGUNITS) specifies
the units for any magnitude specification you provide in the input
arguments. MAGUNITS can be one of

'linear' — specify the magnitude
in linear units

'dB' — specify the magnitude
in dB (decibels)

'squared' — specify the
magnitude in power units

When you omit the MAGUNITS argument, fdesign assumes
that all magnitudes are in decibels. Note that fdesign stores
all magnitude specifications in decibels (converting to decibels when
necessary) regardless of how you specify the magnitudes.

Examples

Bandstop Filtering of Sinusoids

Construct a bandstop filter to reject the discrete frequency band between 3π/8 and 5π/8 rad/sample. Apply the filter to a discrete-time signal consisting of the superposition of three discrete-time sinusoids.

Equiripple FIR Bandstop Filter

Design a constrained-band FIR equiripple filter of order 100 for data sampled at 10 kHz. You can specify constraints on at most two of the three bands: two passbands and one stopband. In this example, constrain the passband ripple to be 0.5 dB in each passband.